[Bug target/104413] _mm_set1_epi8 isn't optimized for SSE2

[crazylht at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104413

--- Comment #1 from Hongtao.liu <crazylht at gmail dot com> ---
Just note pshufb needs SSE3, and it seems reasonable to define a SSE3 broadcast
pattern which generates pxor + pshufb.